Radiocarbon dating on cold-water corals, grain size, Corg, and benthic foraminfera assemblage of two sediment cores from the Ionian Sea

Continuous sedimentary records from an eastern Mediterranean cold-water coral ecosystem thriving in intermediate water depths (~600 m) reveal a temporary extinction of cold-water corals during the Early to Mid Holocene from 11.4-5.9 cal kyr BP. Benthic foraminiferal assemblage analysis shows low-oxygen conditions of 2 ml l**-1 during the same period, compared to bottom-water oxygen values of 4-5 ml l**-1 before and after the coral-free interval. The timing of the corals' demise coincides with the sapropel S1 event, during which the deep eastern Mediterranean basin turned anoxic. Our results show that during the sapropel S1 event low oxygen conditions extended to the rather shallow depths of our study site in the Ionian Sea and caused the cold-water corals temporary extinction. This first evidence for the sensitivity of cold-water corals to low oceanic oxygen contents suggests that the projected expansion of tropical oxygen minimum zones resulting from global change will threaten cold-water coral ecosystems in low latitudes in the same way that ocean acidification will do in the higher latitudes.

对栖息于中等水深（约600米）的东地中海冷水珊瑚生态系统的连续沉积记录研究显示，在全新世早中期（距今11.4~5.9 cal kyr BP），冷水珊瑚曾出现暂时性灭绝。底栖有孔虫（benthic foraminifera）群落分析表明，该珊瑚绝迹时段的同期底层海水溶解氧浓度仅为2 ml·L⁻¹，而珊瑚绝迹前后的底层海水溶解氧浓度可达4~5 ml·L⁻¹。冷水珊瑚灭绝的时间与腐泥质S1事件（sapropel S1）完全吻合，该事件期间东地中海深海盆地曾出现缺氧环境。本研究结果证实，在腐泥质S1事件期间，低氧环境已扩展至爱奥尼亚海本研究站位的较浅水深范围，并最终引发了冷水珊瑚的暂时性灭绝。此项关于冷水珊瑚对海洋低氧环境敏感性的首个实证证据表明，全球变化驱动下热带海洋氧最低带（oxygen minimum zones）的预计扩张，将以与高纬度海域海洋酸化威胁冷水珊瑚生态系统相同的方式，对低纬度地区的冷水珊瑚生态系统构成威胁。